A heat insulator including a stack of inorganic fibers and crimped fibers has recently been developed to improve resilience after compression for efficient packing during transport or the like of the heat insulator in order to increase heat insulating performance (refer to Patent Literature 1, for example). As used herein, the term “resilience” refers to as the ability of a heat insulator to return to its original shape after being compressed.
Furthermore, a vacuum heat insulator recently developed to increase heat insulating performance includes a core member composed of inorganic fibers, such as glass fibers, made by a continuous filament process (refer to Patent Literature 2, for example).
According to a technique described in Patent Literature 2, the inorganic fibers are allowed to have an average fiber diameter greater than or equal to 3 μm and less than or equal to 15 μm in order to suppress, for example, an increase in area of contact between the fibers caused by entanglement of the fibers. This reduces heat conduction between the inorganic fibers.
According to the technique described in Patent Literature 2, the inorganic fibers are also allowed to have an average fiber length greater than or equal to 3 mm and less than or equal to 15 mm in addition to the above-described average fiber diameter. A wet paper-making process involving addition of a dispersant is used to achieve dispersion of the inorganic fibers. This makes the inorganic fibers less likely to align parallel to one another. Consequently, the inorganic fibers tend to have point contact, thus reducing heat conduction between the inorganic fibers.